1. Field of the Invention
The present invention relates to a gate valve cleaning method and a substrate processing system, and more particularly to a method of cleaning a gate valve that brings an atmospheric transfer chamber and an inner pressure variable transfer chamber into communication with each other or shuts them off from each other.
2. Description of the Related Art
A substrate processing system that subjects wafers as substrates to plasma processing is comprised of a process module that houses wafers and subjects them to plasma processing, a load-lock module that transfers each wafer into the process module, and a loader module that removes each wafer from a container housing a plurality of wafers and transfers the wafer to the load-lock module.
In general, the load-lock module of the substrate processing system has a chamber in which a wafer is housed. The load-lock module has a function of opening a gate valve on the loader module side, receiving a wafer in the chamber at atmospheric pressure from a transfer chamber of the loader module, closing the gate valve on the loader module side, evacuating the interior of the chamber to a predetermined pressure, opening a gate valve on the process module side, transferring the wafer into the process module, transferring the wafer out of the process module upon completion of processing, closing the gate valve on the process module side, returning the pressure in the chamber to atmospheric pressure, opening the gate valve on the loader module side, and passing the wafer into the loader module (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2006-128578).
In the load-lock module, however, there may be a case where, in order to improve the throughput of the substrate processing system or due to a problem concerning accuracy of a pressure gauge, the gate valve on the loader module side is opened to pass a wafer without completely returning the pressure in the chamber to atmospheric pressure, i.e. when the pressure in the chamber is lower than the pressure (atmospheric pressure) in the transfer chamber of the loader module. In this case, the atmosphere in the transfer chamber of the loader module flows into the chamber of the load-lock module.
Meanwhile, as shown in FIG. 8A, a conventional gate valve 70 that is disposed between a loader module and a load-lock module and is opened and closed so that the loader module and the load-lock module can be brought into communication with each other or shut off from each other is comprised of a wafer transfer port 71, and a valve element 72 that is driven vertically as viewed in FIG. 8A by a valve element driving mechanism (not shown) so as to open and close the wafer transfer port 71.
In the gate valve 70, in opening and closing the wafer transfer port 71 via the valve element 72, particles 74 produced through rubbing of the valve element 72 against a member 73 that defines the wafer transfer port 71 become attached to, in particular, the valve element 72 (FIG. 8B). As a result, as described above, when the wafer transfer port 71 is opened via the valve element 72 when the pressure in the load-lock module is lower than the pressure in the transfer chamber (atmospheric pressure) of the loader module, the atmosphere inside the loader module flows into the chamber of the load-lock module (FIG. 8C), and the particles 74 attached to the valve element 72 are scattered away through, for example, a disturbance caused by viscous force of the atmosphere, and the scattered particles 74 enter into the chamber of the load-lock module (FIG. 8D). The particles 74 having entered into the chamber of the load-lock module become attached to and accumulated on surfaces of wafers to be transferred, and the particles 74 attached to and accumulated on the wafer cause defects of patterns formed on the wafers. Thus, if the particles 74 enter into the chamber of the load-lock module, the yield and reliability of devices ultimately manufactured from the wafers are decreased.
Conventionally, to prevent the particles 74 from entering into the chamber of the load-lock module, the particles 74 attached to the gate valve 70, in particular, the valve element 72 have been removed in advance through cleaning such as wiping by an operator. However, operation of the substrate processing system has to be stopped for an operator to carry out cleaning such as wiping, and this has significantly decreased the throughput of the substrate processing system.